Glycyl tRNA synthetase regulation. A study of glycycl tRNA synthetase has revealed that two forms of this enzyme are interconverted in yeast cells as part of the operation of a regulatory mechanism that should be vital in governing the synthesis of proteins. The cyclic interconversion is now being studied in vitro. Evolution. Evidence has been obtained that a number of 5'-substituted uracils have a substantial affinity and modest discriminating capacity for certain hydrophobic peptides. A nucleic acid-like homopolymer of one base, 5-benzyl uracil, has been prepared for use in further pursuit of the origin of the genetic code. BIBLIOGRAPHIC REFERENCE: Chao, H.M., Hazel, B., and Black, S.: Binding of uracil derivatives to hydrophobic peptides and sodium dodecyl sulfate. J. Biol. Chem. 251: 6924-6928, 1976.